Sun tans signify status, beauty, sexiness, healthiness therefore, millions of people sunbathe on beaches and decks and in yards, so they can get a sun tan. People even sunbathe at work, during their breaks, trying to improve on their sun tans. Moreover, millions of people take expensive winter vacations to get sun tans.
Tan lines are a by-product of sunbathing. Tan lines are formed at the boundary between the tanned flesh that was exposed to the sun and the untanned flesh that was shielded from the sun by articles of clothing, the bows of glasses, or any object that can shield flesh from the sun. Many sunbathers believe that tan lines detract from the beauty of a sun tan.
Sunbathers typically try to expose as much of their flesh to the sun as possible by wearing bathing suits or shorts while sunbathing. This usually confines tan lines to the more private areas of the body, which are concealed by normal clothing. However, the temple tan lines associated with sunglasses bows are difficult to conceal and are unsightly even in the opinion of the least vain. Who wants to have a white line along each of their temples or on the front of the face or cheeks, commonly referred to as racoon eyes?
In view of the public's recent awareness and concern about adverse short-term and long-term effects on the eyes and visual health due to over exposure of the eyes to the sun and in view of mounting research evidence supporting the occurrence these adverse short- and long-term effects, the necessity of using sunglasses to protect the eyes while sunbathing cannot be ignored.
Studies indicate that most of the damage to the eyes is caused by the ultraviolet (or invisible) portion of the sun's radiation. The sun's radiation is characterized by wavelengths, of which ultraviolet radiation is among the relatively short wavelengths. Ultraviolet radiation occurs at wavelengths between 100 and 400 nanometers while visible light occurs at wavelengths between about 490 and 690 nanometers. Ultraviolet radiation is composed of three segments, designated as A, B, and C. Ultraviolet-C radiation (between 100 and 280 nanometers) is filtered out by the earth's ozone and does not pose a threat. There is much evidence, however, that exposure to both ultraviolet-A (between 315 and 400 nanometers) and ultraviolet-B (between 280 and 315 nanometers) can have adverse short-term and long-term effects on the eyes and visual health.
In 1986, the American National Standards Institute (ANSI) developed voluntary standards for manufacturers of non-prescription sunglasses: cosmetic sunglasses must block at least 70 percent of the ultraviolet-B radiation; general purpose sunglasses must block 95 percent of the ultraviolet-B radiation and most ultraviolet-A radiation; and special purpose sunglasses must block 99 percent of the ultraviolet-B radiation and most ultraviolet-A radiation. The American Optometric Association, the American Academy of Ophthalmology, and the National Society to Prevent Blindness recommend that sunglasses block 99 to 100 percent of both ultraviolet-A and-B radiation and block 75 to 90 percent of the visible light.
The above discussion suggests a conflict between the desire to avoid temple or cheeks sun-tan lines associated with sunglasses bows and the need to wear sunglasses to avoid the adverse short-term and long-term effects on the eyes and visual health due to over exposure of the eyes to the sun.